A. Field of the Invention
The present invention relates generally to the fields of Biology and Chemistry. More particularly, it concerns compositions and methods for controlling the growth of invasive species by endocides.
B. Description of Related Art
Invasive species are major threats to agriculture, natural environments, and public health (Ascunce et al. 2011). The estimated annual damage from invasive species worldwide totals more than $1.4 trillion—five percent of the global economy (The Nature Conservancy, 2013). The principle of the current management strategies of invasive species in the world is mainly restricted to eliminate or eradicate the species by using synthetic herbicide, biological or mechanical applications. Such control measures of invasive species are difficult and often very expensive (Beck et al. 2008). Controlling invasive species and the associated economic and environmental damages amounts to more than $138 billion per year (Pimentel et al. 1999). More than $500 million is spent on residential exotic weed control and an additional $1 billion is invested in non-indigenous weed control on golf courses (Pimentel et al. 1999). In addition to huge expenditures, effectiveness decreases as more species develop resistance to herbicides and public environmental concerns regarding chemical and biological applications increase, it requires a novel philosophy to successfully control the noxious invasive species.
Five of the most aggressive and noxious species in the southeastern United States are representative of different groups of invasive species. They include one fern species: giant salvinia (Salvinia molesta D. S. Mitchell) (family Salviniaceae) from the phyllum Pteridophyta of the kingdom Plantae, two flowering plant species: Brazilian pepper tree (Schinus terebinthifolius Raddi) (family Anacardiaceae) from the order Sapindales and Chinese tallow tree (Triadica sebifera (L.) Small) (family Eurphorbiaceae) from the order Malpighiales of the phyllum Flowering Plants of the kingdom Plantae, and two insect species: the red imported fire ant (Solenopsis invicta Buren) (family Formicidae) from the superorder Endopterygota and the subterranean termite (Reticulitermes flavipes (Kollar)) (family Rhinotermitidae) of superorder Exopterygota of the phylum Arthropoda of the kingdom Animalia. Of these species, giant salvinia is an aquatic species and the others are terrestrial species.
Salvinia Séguier is a genus of floating ferns belonging to the family Salviniaceae Reichenbach and has 10-14 species in the world, particularly in the tropics. Salvinia molesta D. S. Mitchell, known as giant salvinia, water fern, or kariba weed, is native to Brazil. Since 1939, it has invaded lake and river systems in warm climates in the world (Room et al. 1990). At present, giant salvinia is one of the most widespread and environmentally, economically and socially destructive invasive plant species (Schooler et al. 2011). In addition, giant salvinia provides habitat for snails that are intermediate hosts for Schistosoma sp. which parasitize the human intestinal and urinary tracts. The parasitic disease schistosomiasis is also known as snail fever, bilharzia, or bilharziosis, is the second most socioeconomically devastating parasitic disease after malaria.
Giant salvinia is able to double in number and biomass in less than three days under optimal condition and forms dense mats over still waters (Barrett 1989). The plant can regenerate vegetatively even after severe damage or drying for days (Finlayson 1984; Room and Thomas 1986). The explosive growth of S. molesta adversely affects the natural ecological system of the infested region, and it also causes considerable economic damage and sanitation problems. Dense mats of S. molesta reduce dissolved oxygen levels and block all sunlight from penetrating the infested water body. Thus, macrophytes and microscopic algae that form the base of the food chain may die off (Room et al. 1990). The creatures that feed on these may die, too, and so on up the food chain. This pest threatens cultivated aquatic crops, and it can clog irrigation and drinking water lines and foul hydroelectric plants. Salvinia-infested waters cannot be used for boating or other recreational purposes (USDA 2000). Biological, mechanical, and herbicidal control of invasive giant salvinia is very expensive and has not been successful. Since 1980, the tiny salvinia weevil (Cyrtobagous salviniae, Curculionidae) has been introduced into most regions where giant salvinia has invaded (Julien et al. 2009). The weevil is a strict specialist with adults feeding on salvinia buds; the plant is highly susceptible to the insects and thus the weevil has successfully controlled salvinia for years in some regions. But recently it was found that the biological control is incomplete and fitful associated with stochastic flooding events and thus is unpredictable (Schooler et al. 2011). Other attempts to control and eradicate S. molesta through herbicides and mechanical means have failed to achieve their purpose and may cause environmental backlashes due to the introduction of chemicals or bioagents into the environment (Abbasi and Nipaney 1986).
Brazilian pepper tree (Schinus terebinthifolius Raddi) (family Anacardiaceae) is an evergreen shrub or tree (up to 12 m in height) native to South America and was introduced to North America in the 1800s as an ornamental plant. Like poison ivy or sumac of the same family, this species may also cause dermatitis to people with sensitive skin and even respiratory problems during its bloom period. Brazilian pepper tree has extensively infested landscapes in Florida and south Texas and it produces a dense canopy that shades out other plants particularly native species. It is reported that its aqueous extract inhibited the growth and germination of native Florida plants (Morgan and Overhlt 2005). The invasiveness of Brazilian pepper tree can be attributed to its high seed production, high germination rates and dispersal by birds and mammals. Currently, small pepper tree seedlings are controlled by digging or pulling and also by the application of herbicides.
Chinese tallow tree (Triadica sebifera (L.) Small) (family Eurphorbiaceae) is native to China and is now a very invasive species in the southeastern United States. A mature tree may annually produce an average of 100,000 seeds that are spread mainly by birds and water (Jubinsky and Anderson 1996). Under the parent tree, there maybe approximately 15 seedlings per square meter, and its relative frequency of tallow seedlings was greater than that of all species except for sweetgum (Liquidambar styraciflua L.). Various measures, including manual and mechanical, environmental/cultural, chemical, and biological methods have been used to control this invasive species.
Since its introduction from its native South American range in the 1930s, the red imported fire ant (Solenopsis invicta Buren) (family Formicidae) has rapidly widespread throughout the southern United States. It has also recently invaded other regions of the world, including the Caribbean, Mexico, Australia, New Zealand, Malaysia, Singapore, and China (Chen et al. 2009; Ascunce et al. 2011). Unlike other insects in Hymenoptera, the red imported fire ant contains a small fraction of proteins in its venom. About 95% of the fire ant venom consists of alkaloids (primarily 2-methyl-6-alkyl or alkenyl piperidines), which are responsible for the immediate hive formation and the development of the sterile pustule at the sting site (Chen et al. 2009; Hoffman 2010). The pest detrimentally impacts human health, livestock, wildlife, crops, machinery, and electrical equipment (Morrison et al. 2004). The estimated cost of control, medical treatment, and damage to property by fire ant in the United States alone is more than $6 billion annually (Ascunce et al. 2011). An effective measure for control is needed for both ecological and economic reasons.
Eastern subterranean termite (Reticulitermes flavipes (Kollar)) (family Rhinotermitidae) is the most common termite found in North America. This native termite is one of the most economically important wood destroying pests in the United States and it causes billions of dollars in home damage each year. Currently, termite management includes reducing the potential for termite infestation, preventing entry, and chemical control.
The use of defensive chemicals is commonly reported throughout the plant and animal kingdoms. It is known that exceptional success of some invasive species is because they produce toxic secondary metabolites and have negative allelopathic effects on neighboring plants or to protect themselves from microbial attacks and insect/animal herbivory (Quintana et al. 2008; Paudel 2009). Studies on defensive or allelopathic effects of chemicals are mainly to inter-species. Autotoxicity (autointoxication or intraspecific allelopathy in plants) has not been well investigated although it has been hypothesized to exist since the 1970s (McKey 1974; Fowden and Lea 1979; Li et al. 2010). The term was used in plants when a species releases toxic substances into the environmenmt that inhibit or delay germination and growth of the same species (Chou and Lin 1976; Singh et al. 1999). There are few autotoxicity reports in crops and weeds and resulting soil sickness and replanting problems (Singh et al. 1999). These reported autotoxic chemicals had broad-spectrum allelopathic effects and were more effectively inhibited in non-closely-related species in other genera, families or orders than in the parent species (Abdul-Rahman and Habib 1989; Heisey 1999; Batish et al. 2002). However, many of these reports are general allelopathy rather than autotoxicity cases. For example, the effective concentrations of momilactone A and B from rice (Oryza sativa L.) (family Poaceae) to inhibit the seedlings of rice cultivars were 100 and 333 times, respectively of those to inhibit four species of Brassicaceae, Asteraceae, and Fabaceae and five weed grass species of Poaceae (Kato-Noguchi and Ota 2013). Leaf extracts from Leucaena leucocephala de Wit. (family Fabaceae) had significant toxic effects on crop or tree species belonging to other genera of Fabaceae or other families but were not toxic to L. leucocephala seedlings (Chou and Kuo 1986). Minosine isolated from L. leucocephala had more potent inhibitory activity on the seedlings of five species of Brassicaceae, Asteraceae, Fabacreae, and Poaceae but did not show any inhibition on the producing plants at 100 mg/L (Xuan et al. 2006). Leaf and flower extracts of ragweed (Parthenium hysterophorus L.) (family Asteraceae) inhibited the germination and growth of several species in Brassicaceae, Fabaceae, and Poaceae although they showed autotoxic effects to the producing plants (Picman and Picman 1984; Javaid et al. 2007). Alfalfa (Medicago sativa L.) (family Fabaceae) is one of the most extensive investigated and well-known autotoxicity species. It was reported that alfalfa extracts and its phenolics or saponins showed autotoxic effects on seedling growth of alfalfa and allelopathic effects on several crop and weed species of Fabaceae, Poaceae, and Brassicaceae (Wyman-Simpson et al. 1991; Chon et al. 2002). However, alfalfa allelopathy seems to be more severe than autotoxicity (Hedge and Miller 1990). Such non-selectivity or low toxicity of the reported autotoxic chemicals to the parent species over other species limited the development of biocide to selectively control an invasive species. In fact, it has been widely believed that a species can avoid self-toxicity by its endogenous cytotoxic metabolites (Baldwin and Callahan 1993; Wang 1996; Gog et al. 2005; Sirikantaramas et al. 2008a, b). Therefore, studies in autotoxicity have been primarily focused on avoidance of autotoxicity and detoxification mechanisms. To date there is no method or product developed to use any autotoxic chemicals to selectively control the invasive parent species.